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  • Jul 30, 2018
    Carotid Dosimetry and the Risk of Carotid Blowout Syndrome After Reirradiation With Head and Neck Stereotactic Body Radiation Therapy

    Patients with recurrent head and neck cancer have limited options for treatment, and generally poor outcomes.  The standard recommendation is for salvage surgery, but many patients are not eligible for this due to comorbidities, general medical deconditioning, or location of recurrence.  However, there has been concern with the role of reirradiation given retrospective reports of long term toxicity, and specifically the concern for carotid blowout syndrome (CBOS).  CBOS is defined as a complication of head and neck cancer in which the carotid artery or one of its major branches ruptures.  It is most often fatal.  SBRT is more attractive than conventionally fractionated treatment for a number of reasons including decreased acute toxicity and decreased treatment time.  Some small retrospective studies have previously suggested increased risk of CBOS for SBRT (8-17%) versus conventionally fractionated treatment (1-4%), as well as higher risk if >180 degrees of the carotid artery is encased.  This study examined whether there is any relation between SBRT and CBOS in the setting of reirradiation based on DMax, mean dose to the carotid, and additional risk factors such as degree of carotid encasement, skin involvement, and ulceration/necrosis. This is a single institution retrospective study of 75 patients and 150 carotid arteries.  All patients had previous conventionally fractionated head and neck radiation with a mean dose of 70Gy.  Their prior radiation doses, carotid hotspots, or carotid coverage were not accounted for in this study.  It only examined the SBRT reirradiation dose and hotspots.  Patients were treated to 40-50Gy in 5Fx delivered every other day.  A minority of patients (10.7%) had 2 or more courses of SBRT reirradiation and for these patients their cumulative SBRT dose was accounted for.  The median Dmax for the following volumes was: D0.1cc=40.8Gy, D1cc=26.8Gy, D2cc=15.4Gy.  The mean carotid dose was 15Gy, and median PTV size 39.3 cm^3. Interestingly this study only found a total of 4 carotid bleeding events (5.3%), which is lower than the previously reported 8-17% in the SBRT setting.  Of these, two were mucosal bleeds that were successfully embolized and 2 were truly fatal CBOS (2.6%).  This is within the range of 1-4% previously reported for conventional fractionation.  There was no true significant association between DMax, Dmean, or additional risk factors such as necrosis or carotid encasement.  There was however a trend (p=0.08) towards increased risk of bleeding with D0.1cc>47.6Gy.  Of note there was a true minority of patients who had carotid encasement >180 degrees (16%); the large majority (78.7%) had 0 carotid encasement.  The same is true for skin invasion (only 5.3%) and ulceration (9.3%).  These numbers are too small to form any real conclusions about safety of irradiating in these settings.  Additionally, it must be accounted for that this is a retrospective study that did not account for overlapping hotspots from previous radiation. Overall, this study does provide a preliminary reassurance that carotid reirradiation, especially in the SBRT setting, may pose less of a threat than previously thought for CBOS.  This opens the door for a modality of treatment that is often a head and neck patient’s only choice in a challenging setting of recurrence, especially if they have poor performance status or other comorbidities.  It cautions to proceed carefully and potentially limit D0.1CC to <47.6Gy.  More remains to be investigated for the true safety threshold of reirradiation, especially in the setting of overlapping hotspots from previous treatment, and carotid encasement. 

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    Journal & Date: Int J Radiation Oncol Biol Phys, Vol. 101, No. 1, pp. 195-200, 2018
    Key Institution: UPMC Cancer Center, Pittsburgh PA
    Keywords: Carotid blowout, head and neck cancer, reirradiation, SBRT, maximum dose, mean carotid dose, carotid encasement, concurrent cetuxumab

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